1. Field of the Invention
The invention relates to an oil pump provided in a vehicle. More particularly, the invention relates to a vehicle oil pump that has a structure in which a drive gear that drives the oil pump rotates in one direction when the vehicle travels forward and rotates in the opposite direction when the vehicle travels backward.
2. Description of the Related Art
In a power transmitting apparatus provided in a vehicle, hydraulic pressure of oil supplied to lubricating mechanisms and clutches that are driven by hydraulic pressure is generated by an oil pump that is a hydraulic pressure generating mechanism. A related oil pump is configured to be driven by a rotating shaft that rotates in a certain direction, such as an output shaft of an engine, for example, so the oil pump is always driven in a certain direction. However, in an electric vehicle, for example, an electric motor that serves as a driving source rotates in one direction when the vehicle travels forward and rotates in the opposite direction when the vehicle travels backward. Therefore, when an oil pump is driven by a rotating shaft of the electric motor, the oil pump will end up rotating in the opposite direction when the vehicle travels backward, for example, and as a result, a sufficient amount of oil may not be able to be supplied when the vehicle travels backward. This problem is not limited to the electric vehicle described above. That is, with a structure in which an oil pump is driven by a rotating shaft that rotates in one direction when the vehicle travels forward and rotates in the opposite direction when the vehicle travels backward, such as an output shaft of a vehicular power transmitting apparatus, the necessary oil is unable to be supplied when the oil pump rotates in the opposite direction while the vehicle is traveling backward, for example.
Regarding this, Japanese Patent Application Publication No. 10-217787 (JP-A-10-217787) describes technology that always communicates an intake port with a tank, and a discharge port with an operating chamber of a hydraulic clutch, by switching the discharge port and the intake port using a switching valve that switches an oil passage according to the direction of travel of the vehicle, in a structure in which oil is discharged from an oil pump in one direction when the vehicle travels forward and is discharged from the oil pump in the opposite direction when the vehicle travels backward in a four-wheel-drive vehicle.
However, with the structure of the four-wheel-drive vehicle described in JP-A-10-217787, the need to provide the switching valve and the like complicates the structure and increases the number of parts, which in turn increases the manufacturing cost.